ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the Fiscal Year Ended December 31, 2013

or

¨

TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from
to

Commission File Number 1-6249

WINTHROP
REALTY TRUST

(Exact name of Registrant as specified in its certificate of incorporation)

Ohio

34-6513657

(State or other jurisdiction of

incorporation or organization)

(IRS Employer

Identification Number)

7 Bulfinch Place, Suite 500, Boston, Massachusetts

02114

(Address of principal executive offices)

(Zip Code)

(617) 570-4614

(Registrants telephone number, including area code)

Securities registered pursuant to Section 12(b) of the Act:

Title of Each Class

Name of Exchange on Which Registered

Common Shares, $1.00 par value

New York Stock Exchange

9.25% Series D Cumulative Redeemable Shares, $1.00 par value

New York Stock Exchange

Securities registered pursuant to Section 12(g) of the Act: None

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes ¨ No x

Indicate by check mark
if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act. Yes ¨ No x

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by
Section 13 or 15(d) of the Securities and Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for at
least the past 90 days. Yes x No ¨

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required
to be submitted and posted pursuant to Rule 405 of Regulation S-T (§ 232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such
files). Yes x No ¨

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to
the best of registrants knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K. ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See
the definitions of large accelerated filer, accelerated filer, and smaller reporting company in Rule 12b-2 of the Exchange Act. (Check one):

Large accelerated filer

¨

Accelerated filer

x

Non-accelerated filer

¨ (Do not check if a smaller reporting company)

Smaller reporting company

¨

Indicate by check mark whether the registrant is a shell company (as defined in Exchange Act Rule
12b-2). Yes ¨ No x

As of March 1, 2014, there were 36,409,710 Common Shares outstanding.

At June 30, 2013, the aggregate market value of the Common Shares held by non-affiliates was $394,931,691.

DOCUMENTS INCORPORATED BY REFERENCE

Portions of the registrants definitive Proxy Statement for the Annual Meeting of Shareholders, which is expected to be filed with the Securities and
Exchange Commission within 120 days after the Registrants fiscal year ended December 31, 2013, are incorporated by reference into Part III hereof.

EXPLANATORY PARAGRAPH

This Form 10-K Amendment No.1 is being filed solely for the purpose of attaching as Exhibits 99.5 and 99.6 the audited financial statements of
Vintage Housing Holdings LLC and 701 Seventh WRT Investor LLC and Subsidiaries as required by Rule 3-09 of Regulation S-X and to amend the Exhibit Index accordingly. This Form 10-K Amendment No. 1 has not been updated for events or information
subsequent to the date of filing of the original Form 10-K for the year ended December 31, 2013 (the Original 10-K). Accordingly, this Form 10-K Amendment No. 1 should be read in conjunction with the Original 10-K and the
registrants other filings with the Securities and Exchange Commission. Except as described above, no other changes have been made in this Amendment to modify or update the other disclosures presented in the Original 10-K.

ITEM 15  EXHIBITS AND FINANCIAL STATEMENT SCHEDULES

(a) Financial Statements and Financial Statement Schedules.

(1) Financial Statements:

The following documents were
filed as a part of the Original Filing:

Report of Independent Registered Public Accounting Firm.

Consolidated Balance Sheets - December 31, 2013 and 2012.

Consolidated Statements of Operations and Comprehensive Income - For the Years Ended December 31, 2013, 2012 and 2011.

Consolidated Statements of Shareholders Equity - For the Years Ended December 31, 2013, 2012 and 2011.

Consolidated Statements of Cash Flows - For the Years Ended December 31, 2013, 2012 and 2011.

Notes to Consolidated Financial Statements.

(2) Financial Statement Schedules:

The following
financial statement schedules were filed as part of the Original Filing and should be read in conjunction with the Consolidated Financial Statements of the Registrant:

Schedule III - Real Estate and Accumulated Depreciation.

Schedule IV - Mortgage Loans on Real Estate.

All Schedules,
other than III and IV, are omitted, as the information is not required or is otherwise furnished.

The Trusts unconsolidated joint ventures, 701
Seventh WRT Investors LLC and Vintage Housing Holdings LLC, meet the definition of a significant subsidiary under S-X 210.1-02 (w) and financial statements for these entities are filed as part of this Form 10-K Amendment No. 1.

(b) Exhibits.

The exhibits listed on the Exhibit Index
are filed as a part of this Report or incorporated by reference.

SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, as amended, Winthrop Realty Trust has duly caused this report
to be signed on its behalf by the undersigned, thereunto duly authorized.

WINTHROP REALTY TRUST

Dated: March 31, 2014

By:

/s/ Michael L. Ashner

Michael L. Ashner

Chief Executive Officer

Dated: March 31, 2014

By:

/s/ John A. Garilli

John A. Garilli

Chief Financial Officer

(Principal Financial Officer and Principal Accounting Officer)

Exhibit

Description

PageNumber

3.1

Second Amended and Restated Declaration of Trust as of May 21, 2009 - Incorporated by reference to Exhibit 3.1 to the Trusts Quarterly Report on Form 10-Q for the period ended June 30, 2009.



3.2

By-laws of Winthrop Realty Trust as amended and restated on November 3, 2009 - Incorporated by reference to Exhibit 3.1 to the Trusts Current Report on Form 8-K filed November 6, 2009.



3.3

Amendment to By-laws - Incorporated by reference to Exhibit 3.1 to the Trusts Current Report on Form 8-K filed March 6, 2010.



4.1

Form of certificate for Common Shares of Beneficial Interest. Incorporated by reference to Exhibit 4.1 to the Trusts Annual Report on Form 10-K for the year ended December 31, 2008.



4.2

Agreement of Limited Partnership of WRT Realty L.P., dated as of January 1, 2005 - Incorporated by reference to Exhibit 4.1 to the Trusts Current Report on Form 8-K filed January 4, 2005.



4.3

Amendment No. 1 to Agreement of Limited Partnership of WRT Realty, L.P., dated as of December 1, 2005 incorporated by reference to Exhibit 4.4 to the Trusts Form 10-K filed March 15, 2012.



4.4

Amendment No. 2 to Agreement of Limited Partnership of WRT Realty, L.P., dated as of November 28, 2011 - Incorporated by reference to the Trusts Current Report on Form 8-K filed November 28, 2011.



4.5

Amendment No. 3 to Agreement of Limited Partnership of WRT Realty, L.P., dated as of March 23, 2012 - Incorporated by reference to the Trusts Current Report on Form 8-K filed March 23, 2012.



4.6

Amended and Restated Certificate of Designations of 9.25% Series D Cumulative Redeemable Preferred Shares of Beneficial Interest - Incorporated by reference to the Trusts Current Report on Form 8-K filed March 23,
2012.



4.7

Form of Specimen Certificate for the 9.25% Series D Cumulative Redeemable Preferred Shares of Beneficial Interest - Incorporated by reference to Exhibit 4.2 to Trusts Form 8-A filed with the Securities and Exchange Commission
on November 23, 2011.



4.8

Indenture, dated August 6, 2012 between the Trust and The Bank of New York Mellon, as trustee - Incorporated by reference to the Exhibit 4.1 to the Trusts Current Report on Form 8-K filed August 9, 2012.



4.9

First Supplemental Indenture, dated August 15, 2012, between the Trust and the Bank of New York Mellon, as trustee and collateral agent - Incorporated by reference to Exhibit 4.1 of the Trusts Current Report on Form 8-K filed
August 15, 2012.



10.1

Stock Purchase Agreement between the Trust and FUR Investors, LLC, dated as of November 26, 2003, including Annex A thereto, being the list of Conditions to the Offer - Incorporated by reference to Exhibit 10.1 to the Trusts
Current Report on Form 8-K filed December 1, 2003.



10.2

Third Amended and Restated Advisory Agreement dated February 1, 2013, between the Trust, WRT Realty L.P. and FUR Advisors LLC - Incorporated by reference to Exhibit 10.1 to the Trusts Current Report on Form 8-K filed
February 4, 2013.



10.3

Exclusivity Services Agreement between the Trust and Michael L. Ashner - Incorporated by reference to Exhibit 10.4 to the Trusts Current Report on Form 8-K filed December 1, 2003.



10.4

Amendment No. 1 to Exclusivity Agreement, dated November 7, 2005 - Incorporated by reference to Exhibit 10.7 to the Trusts Current Report on Form 8-K filed November 10, 2005.



10.5

Amendment No. 2 to Exclusivity Agreement, dated February 1, 2013 - Incorporated by reference to Exhibit 10.2 to the Trusts Current Report on Form 8-K filed February 4, 2013.



10.6

Covenant Agreement between the Trust and FUR Investors, LLC - Incorporated by reference to Exhibit 10.5 to the Trusts Current Report on Form 8-K filed December 1, 2003.



10.7

Amendment No. 1 to Covenant Agreement, dated February 4, 2013 - Incorporated by reference to Exhibit 10.3 to the Trusts Current Report on Form 8-K filed February 4, 2013.



10.8

Winthrop Realty Trust 2007 Long Term Stock Incentive Plan - Incorporated by reference to the Trusts Definitive Proxy Statement on Schedule 14A filed with the Securities and Exchange Commission on March 30, 2007.



10.9

Amended and Restated Loan Agreement, dated as of March 3, 2011, between WRT Realty L.P. and KeyBank, National Association. Incorporated by reference to Exhibit 10.19 to the Trusts Annual Report on Form 10-K for the year ended
December 31, 2011.



10.10

Guaranty from Winthrop Realty Trust and certain of its Subsidiaries in favor of KeyBank, National Association. Incorporated by reference to Exhibit 10.20 to the Trusts Annual Report on Form 10-K for the year ended
December 31, 2011.



10.11

Restricted Share Award Agreement, dated February 1, 2013, between Winthrop Realty Trust and Michael L. Ashner - Incorporated by reference to Exhibit 10.4 to the Trusts Current Report on Form 8-K filed February 4, 2013.



10.12

Restricted Share Award Agreement, dated February 1, 2013, between Winthrop Realty Trust and Carolyn Tiffany - Incorporated by reference to Exhibit 10.4 to the Trusts Current Report on Form 8-K filed February 4, 2013.